Insulator



C. B. VAN ATTA 1,832,157

INSULATOR Filed Feb. 17, 1927 Nov 17, 1931.

as .f

' ed or roughened surfaces,

Patented Nov. 17, 1931 UNITED STATES PATENT OFFICE CLOYD '.B. VAN ATTA, OF BALTIMORE, MARYLAND, ASSIGNOR TO LOCKE INSULATOR CORPORATION, OF BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND INSULATOR Application led February 17,

The invention relates to high tension insulators, particularly those of the suspension type V.and has special reference to insulators embodying a dielectric body having a stem at one side and a recess at the other, the formery carrying a cap and the other having a pin cemented thereinto.

The principal object of the invention, generally stated, is toimprove the construction of insulators of this type whereby to increase the mechanical and electrical strength thereof and consequently avoid puncture or ruture under strain conditions.

t is well known that in insulators of this type the pin has its upper end flared outwardly to a fairly sharp or abrupt edge. This is true regardless of whether the pin be of the single step type or whether it be formed with a plurality or series of steps. The pin is of course cemented within the recess in the underside of the porcelain body and the walls of the recess are generally sand- I ed or otherwise Toughened to insure efficient holding action ofthe cement.' Clearly, when the pin is embedded within the mass of cement and the cement firmly locked to the porcelain body by its engagement with the sandgreat solidity results. This is objectionable for the reason that when temperature changes occur strains are set up owingto thediiferences between the coefficients of expansion of porcelain, cement and the metal of the pin. Even though pins have been coated vwith an elastic material, such as asphaltum dissolved in benzol, there is insuiiicient give or yield inthe parts to permit the unequal expansion and contraction thereof without the bringing of severe strains upon the various parts of the insulator. It also seems to make no difference whether the cement be permitted to set at room temperature or at an elevated temperature such for instance as the maximum to which the insulator may be subjected in service, serious strains being invariably produced at a subsequent time when the temperature fluctuates. It has been discovered by actual test that when an insulator of this type is hilled, thecontraction of the pin, whichr's'much greater than that of the cement owing 1927. Serial No. 168,974.

to the differences in the coeiiicients of expansion, will cause the maximum strain to occur at the edge of the step or head, if only one is provided, or at the edge of the topmost step if a series are used. When an insulator constructed in this manner is subjected to a certain mechanical pull or load, which may or may not be in excess of that to which it is subjected in service, the crushing strains at the edge of the step or edge of the topmost step will cause the procelain to rupture at a point or points opposite the end of the pin whereas the normal point of rupture under excess strain should be at the edge of the cap.

It is with the above facts in view that I have designed the present invention which has for an importantobject the provision of a pin so constructed, as compared with the ordinary ones, as to relieve or avoid the bringing of excess strain at its edge upon contraction of the insulator parts asthe result of temperature changes.

Anothercbject of the invention is to provide an insulator and pin therefor in which the pin is of such formation as todistribute the internal strains and stresses within the insulator `throughout the entire mass of cement which embeds the pin, this distribution of forces preventing concentration of strains and consequent rupture of the porcelain.

A more specific object of the invention is to provide an insulator having the improved pin and in which the pin is preferably coated entirely or substantially throughout its cement contacting area to permit slippage so that the parts may accommodate themselves so as to distribute uniformly whateverl strains are produced upon relative movement of the parts as the result of expansion and contraction under different thermal conditions.

To the attainment of the foregoing and other objects and advantages, the invention preferably consists in the detailed construction and the arrangement and combination to be hereinafter more fully described and claimed, and illustrated in the accompanying drawings in which:

Figure l is a diagrammatic view illustrating the relation of the pin bearing surface 10 set at steaming temperature, approximately insulator constructed in the manner above and cement bearing surface under the temperature condition existing during setting of the cement,

igure 2 is a similar view showing the relative positions of the coacting surfaces of the pin and cement at a greatly reduced temperature, n

Figure 3 is a cross sectional view through a portion of an insulator eferring more particularly to the drawings, and especially merals l and 2 deslgnate, pin head and the adjacent portion of the cement which embeds the pin within the porcelain body 3. The lines AB and BC lie along the contacting surfaces. In ordinary practice, the cement employed for embedding the pin withinthe recess in the porcelain body is respectively, the

125 F. When setting of the cement occurs the surfaces of the cement and pin conformingly engage and the lines AB and BC coincide, as illustrated in Figure 1. When an indicated is subjected to a temperature of, .say,25 to 125 F. lower than that at which the cement was set, the cement, which would under ordinary conditions shrink or contract, is revented from doi so because it is firmlylljionded to the porce ain land the porcelain has a much lower coeicient of expansion than the cement. The normal shrinkageV of the cement is prevented whereas the pin does conf tract as the result ofthe temperature change and the surface of the pin shrinks away from the surface of the cement. This is true regandless of whether the cement is set at an elevated temperature or at normal room temperature.

en contraction occurs in an insulator when the temperature thereof is, say, 125O F. below steaming temperature, or at 0 F., the bearing surface of the step, or top step if more than one are present, first takes the approximat position indicated by the lines AB and VBC 1n Figure 2, the pm binding at BD. The point D is approximate and its location varies with the degree or extent of temperature change. As the load becomes greater and before uniform bearing can be reached along cement between the nary point D must be crushed. The force recement varies with the If the cement is soft under a' strain less than at'point E, Figure porcelain. The cement Figures l and 2, the nuremembered that there is a finally, under service load, crumbles in the area BD and after this takes place the entire bearing surface of the pin comes in contact with the cement. The damage, however, has been done and while the slight crack or rupture of the porcelain at this point may not appreciably affect the combined mechanical and electrical strength of the insulator in some respects it nevertheless greatly reduces the puncture value. c

In carrying out the present invention, reference is made to ,Figure 3 which embodies` the above described principle and wherein the numeral 4-'designates a portion of the porcelain body of an 4insulator having the usual upstanding stem 5 within which is formed a recess (i. The stem 5 carries the usual cap 7 and cemented into the recess is the. pin 8 having a head comprising a plurality of tapered Haring o r conoidal steps 9, l() and 11. To avoid the concentration of strains described in connection with Figures l and 2, I have found it merely necessary to bevel oli'ythe edge of the upper step 9 as shown the substantially obviously of less diameter than the other steps. The corners are rounded off as at 13 instead of being left sharp. lVhile it may not be essential it is preferable that the head of the pin be dipped or otherwise treated to provide a coating thereon of yieldable elastic ymaterial such. for instance, as asphaltum Vin order to facilitate slippage of the pin with respect to the cement within which it is embedded. In the operation of the invention it will be apparent that the strains occurring as the result of relative movement of the pin, porcelain and cement under different thermal conditionsrwill be avoided to a great extent. That is to say, there will be no excessive crushing force applied at any area correspondingr to that between the points B and in Figure 2. The cement will therefore not crumble away inasmuch as a uniform bearing surface may be had even at the beginning of a pull. Any strains or stresses are distributed instead of beingr localized at the point opposite the uppermost edge of the pin and danger of rupture of the porcelain will be eliminated.

As the edge of the uppermost step is beveled oit it is clear that there will be less opposition to the longitudinal. contraction of the pin when cooling of the insulator occurs and the strains are therefore permitted to come upon the successi ve other steps instead of 'being concentrated at the area of contact of the uppermost step with the cement.

In addition to the thermal action above described, or aside from it. it is of course to be mechanical load on the insulator while in service. By test and computation it has been found that in the case'of an insulator embodying a three step pin such` as that disclosed, the major portion Vof the load, namely approximately 42% is sustained by the uppermost step, the intermediate and lowermost steps taking a 5 proportionately smaller share, actually about 33% and :25% respectively. It is Well known that cement is capable of yielding to a greater extent than porcelain, from which it follows that wherever the cement is the thinnest there is bound to be the maximum strain. In accordance with my invention the reduction of they diameter of the topmost step must reduce the strain transmitted to the porcelain as there is a. corresponding increase in the thickness of the cement mass embedding this step of reduced diameter. The intermediate and lowermost steps need not be of the same diameter themselves though as there is less pressure exerted by them than by the uppermost step they are shown as of the same diameter as there is no particular reason for relieving any stress other than that at the uppermost step as specified. Clearly, in the use of my invention all forces will therefore be uniformly distributed throughout the mass of cement.

While I have shown and described the preferred embodiment of the invention, it should be understood that I reserve the right to make suci changes in the details, particularly in the matter of size and shape, as will not depart from the spirit of the invention or the scope of the claims hereunto appended.

Having thus described the invention,

claim:

l. In an insulator, a porcelain body having an rupstanding stem thereon and formed Wit-h arecess, a cap iitting upon and secured to the stem, and a pin cemented Within the recess, the pin having a head formed with a 'flaring endmost step With a beveled and rounded edge, the pin being further formed With additional steps, the endmost step being of less diameter than said other steps.

Q. In an insulator, a porcelain body having an upstanding stem thereon formed with a recess opening out to its underside, a cap fitting upon and secured to the stem, a pin located within the recess and a mass of cement embedding the pin within the recess, that portion of the pin extending Within the recess having a head formed with a plurality of steps the step nearest the closed end of the recess being of less diameter than the others and having a c vlindrical periphery with a rounded edge whereby the thickness of the cement mass opposite this step of reduced diameter Will be greater than the thickness of the mass of cement surrounding the other steps.

In testimony (yjvlliereof I affix my signature.

OYD B. VAN ATTA. 

